As representative examples of rubber-reinforced graft copolymers, particularly rubber-reinforced graft copolymers prepared through emulsion polymerization, there are ABS, MBS, ASA, ATM, etc. These are prepared by graft-copolymerizing a variety of monomers, while considering dispersibility of a matrix phase, to an outer shell of a core of a rubber prepared through conventional emulsion polymerization. In particular, ABS is prepared by graft-copolymerizing a styrene-acrylonitrile copolymer (PSAN) to an outer shell of poly butadiene latex as a core. In particular, ABS products thereamong have superior impact resistance and heat resistance, process properties such as chemical resistance, and superior appearance properties, thus being broadly used as exterior materials of vehicles, or materials of housings of home appliances and toys.
In particular, in order to produce ABS having superior thermal properties (heat deflection resistance, HDT), namely, heat resistance as in materials of vehicles, a resin (heat resistant SAN) having a high glass transition temperature (Tg) is prepared through emulsion polymerization or solution polymerization, and a final product may be prepared by mixing and melt-blending such that a rubber-reinforced graft copolymer in which SAN is graft-copolymerized through emulsion polymerization has constant rubber content.
As representative monomers used in a heat-resistant resin having high glass transition temperature, there are styrene-based derivatives such as α-methyl styrene (AMS) and imide based monomers such as N-phenylmaleinimide (PMI), etc. These exhibit enhanced heat resistance as a ratio of AMS used in a resin increases, but there are many problems in a polymerization step to prepare a resin.
Accordingly, in order to address problems due to application of AMS, a variety of methods have been tried. In U.S. Pat. No. 2,908,666, it was tried to enhance impact resistance, environmental stress crack resistance (ESCR) and heat resistance, by grafting an AMS monomer and an acrylonitrile monomer to polydiene rubber latex, but polymerization took a long time, information regarding a polymerization conversion rate was not described, and it is difficult to recognize that superior impact strength was realized.
In addition, in U.S. Pat. No. 5,266,642, polymerization was performed in the presence or absence of a rubber polymer to increase polymerization speed, when an AMS based polymer was prepared through emulsion polymerization, but rubber polymer content was very low, polymerization conversion rate was not high and, particularly, impact resistance and thermal properties of a resin were not referred.
In addition, U.S. Pat. No. 4,774,287 discloses a method wherein superior thermal properties are exhibited at high temperature and AMS decomposition in high process temperature is prevented, but does not describe superior polymerization conversion rate, reaction time, or impact resistance.
Accordingly, there is still a need for rubber polymer and graft copolymer technology which may decrease polymerization time while effectively providing impact resistance, thermal properties, etc.